Third generation partnership project (3GPP) mobile communication systems based on a wideband code division multiple access (WCDMA) radio access technology are widely spread all over the world. High-speed downlink packet access (HSDPA) that can be defined as a first evolutionary stage of WCDMA provides 3GPP with a radio access technique that is highly competitive in the mid-term future. However, since requirements and expectations of users and service providers are continuously increased and developments of competing radio access techniques are continuously in progress, new technical evolutions in 3GPP are required to secure competitiveness in the future. Reduction of cost per bit, increase of service availability, flexible use of frequency bands, simple structure and open interface, proper power consumption of a user equipment (UE), and the like are defined as requirements.
In general, there are one or more cells within the coverage of a base station (BS). There may be a plurality of UEs in a cell. A UE is generally subjected to a random access procedure to access a network. The random access procedure is performed by the UE for the purposes of initial access, handover, scheduling request, timing alignment, etc.
The random access procedure can be classified into a contention based random access procedure and a non-contention based random access procedure. A major difference between the two random access procedures lies in whether a random access preamble is dedicatedly assigned to one UE. In the non-contention based access procedure, since a UE uses only the random access preamble dedicatedly assigned to the UE, contention (or collision) with another UE does not occur. The contention occurs when two or more UEs attempt the random access procedure by using the same random access preamble through the same resource. In the contention based random access procedure, there is a possibility of contention since random access preambles used by the UEs are randomly selected.
As described above, when it is considered that the random access procedure is initiated for various reasons and is classified into the contention based random access procedure and the non-contention based random access procedure, the random access procedure may be ineffective if a random access response in use has only one configuration.
For example, in the non-contention based random access procedure, the UE can transmit uplink data by using uplink radio resource assignment information included in the random access response. However, if the UE does not have the uplink data, the uplink radio resource assignment information is unnecessary.
Accordingly, there is a need for a method capable of utilizing radio resources further effectively in a random access procedure.